1. Field of the Invention
The present invention relates to a pressure vessel, and more particularly to a pressure vessel for water treatment equipment. This vessel has thin sidewalls made from a thermoplastic material which are wrapped with a filament type material for added strength and integrity. The entire vessel is then wrapped in layers of insulating foam and sheet material. The thin sidewalls of the pressure vessel have one or more receiving pockets and a structural insert means bonded or otherwise adhered into each of the receiving pockets. The receiving pockets with the structural insert means form localized areas of increased thickness in the thin sidewalls of the vessel. A port or aperture is formed in the localized areas of increased thickness for receiving spouts or other fittings.
2. Description of the Prior Art
Modern material handling applications require that a pressure vessel safely contain various corrosive and non-corrosive fluids at high pressures and temperature. The prior art pressure vessels capable of withstanding these high working pressures and temperatures unusually have massive, commonly metal, wall structures that limit the vessel's use to commercial or heavy duty industrial applications. Since these vessels have thick and heavy sidewall structures they can easily accommodate side ports that adequately support various fittings without leakage. However, as indicated above, the use of these heavy metal vessels is restricted and frequently their manufacture is difficult and expensive.
The prior art also includes pressure vessels designed to overcome the disadvantages of these massive metal vessels. One such pressure vessel is the vessel disclosed in U.S. Pat. No. 3,874,544 to Harmon. This vessel has a composite outer shell of continuously wound glass filaments impregnated with a thermosetting resinous material and an inner liner made of blow molded plastic. Its sidewalls are relatively thin and light, making it easy to handle and construct. However, this vessel only includes top and bottom ports with fittings; it does not include any ports in its sidewalls. Attempting to place a fitting in a port in the thin sidewall of such a vessel presents significant and serious problems. First, the thin sidewall does not have sufficient material thickness to be property threaded and accordingly cannot directly received a threaded fitting. Second, the thin sidewall is not thick enough to adequately support a pipe or the like which could then receive a threaded fitting. In general, the aperture or port in such a thin sidewall has an annular wall surface. The outer surface of the pipe or fitting must be bonded or sealed to this annular wall surface in order to prevent leaks from within the vessel. Since the contact area between the annular wall surface and the insert is small, a good seal is not possible. Also, since the contact area is small, the structural integrity of the seal is weak and easily broken or cracked by even slight contact with the external portion of the fitting. Finally, the thin sidewall of the vessel is weakened in the area of the port and may fracture or fail in this area.
Some prior art vessels have complicated component arrangements around the ports in their sidewalls. For example, U.S. Pat. No. 868,548 to Griffin discloses a compressed air tank with a pipe that extends into the tank through a plate which is bolted to the side of the tank's outer shell; a cone is bolted to the plate; and a rubber bag is disposed inside the tank. A cap-shaped nut is screwed to the lower end of the pipe, and the cone is clamped to a thickened portion of the rubber bag to secure it. This structure is a mechanically connected arrangement of parts and not a portion of a one-piece, integral unit. Neither the cone nor the nut binds with or fuses into the thickened portion of the rubber bag. The arrangement only serves to clamp and secure the rubber bag, not to increase the thickness of the metal shell or to support the pipe.
U.S. Pat. No. 2,273,736 to Raymond et al. discloses a pressure vessel with a fitting at a port in its sidewall. The fitting is a rounded metal piece with a flat top and countersunk base. Since the pressure vessel has thick and massive sidewalls, the fitting does not serve to increase the thickness of these sidewalls. The fitting's only function is to provide a passageway through the layers of metal ribbon that form a portion of the sidewall of the vessel. The top of the fitting projects beyond the outer surface of the vessel, providing a discontinuity in this surface that limits the vessel's application.
The pressure vessel of the present invention avoids the problems of the prior art pressure vessels. The pressure vessel of the present invention is light weight, easy to manufacture, provides for fittings in the sidewall and is adaptable for residential use. It has a thin thermoplastic liner with at least one receiving pocket in the sidewall. An insert or plug means is adhered or bonded into each of the receiving pockets so that its surface is flush with the surface of the liner. A reinforcing dome means is placed at both ends of the liner to provide added strength over these surfaces. A filament winding is wrapped around the liner, over the insert means and over at least a portion of the dome means. Layers of foam, sheet or other insulating material can be placed over the filament winding to provide temperature control for the fluid contained within the vessel if that function is necessary. Since the thin sidewalls of the pressure vessel have localized areas of increased thickness which are integral with the inner liner, apertures or ports can be opened through these areas and appropriate fittings placed in the ports do not weaken the thin sidewalls and do not create leaks of fluids stored within the vessel. These localized areas protrude toward the inside of the inner liner, maintaining a contiguous smooth surface over the length of the sidewall.